Rocks - introduction and importance - class-VIII

Igneous rock (derived from the Latin word ignis meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava.

Gypsum Products and Properties as a Building Material for Construction. Gypsum is one of the widely used construction material mainly in interior designing. Gypsum is used as surface materials. Its application is prominent in wall and ceiling construction.

Lithification is the process by which sediments combine to form sedimentary rocks. Compaction is a consolidation of sediments due to the intense pressing weight of overlying deposits. With compaction, sediment grains get squished together, reducing the size of the original pore space that divided them.

Plaster of paris originally was made from the extensive gypsum deposits of Montmartre in Paris.

Plaster of paris, consists of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Known since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found near Paris.

The igneous rocks are called primary rocks because these were originated first of all rocks during the formation of the upper crust of the earth on cooling, solidification, and crystallization of hot and liquid magmas after the origin of the earth. Thus, all the subsequent rocks were formed, whether directly or indirectly, from the igneous rocks in one way or the other.

• Rocks formed after evaporation of water are called evaporites. Gypsum is an example of evaporites.
  
• Plaster of Paris is manufactured from gypsum and thus it is a secondary product hence cannot be the right answer here.
• Thus option B ie gypsum is the right answer.

• Rocks formed by the cooling of molten rock are called igneous rocks. Among the given options only granite is an igneous rock while rest 3 are sedimentary ricks.
• Hence option C is correct.

The word igneous has been derived from a Latin word 'ignis', meaning thereby fire. The igneous rocks are formed due to cooling, solidification, and crystallization of hot and molten materials known as magmas and lavas. They were originated first of all the rocks during the formation of the earth.

Among the three major types of rock, fossils are most commonly found in sedimentary rock. Unlike most igneous and metamorphic rocks, sedimentary rocks form at temperatures and pressures that do not destroy fossil remains.

Chemical sedimentary rocks are formed by the precipitation of minerals from water. Precipitation is when dissolved materials come out of water. They are typically made up of the minerals halite (calcium chloride, or rock salt) and gypsum (calcium sulfate).

B. Minerals

Native gold is an element and a mineral. It is highly prized by people because of its attractive color, resistance to tarnish, and its many special properties - some of which are unique to gold. Its rarity, usefulness, and desirability make it command a high price. 

The term mineral is sometimes used in reference to natural earth (non-living) resources, and thus, in a non-scientific sense, petroleum resources are mineral resources and deposits of petroleum are often called mineral deposits. Coal, sands, gravel, and such would also be considered a mineral resource in this particular usage, even though coal is a rock, not a mineral, and the others are mixes of multiple minerals and/or rocks and not, strictly speaking, minerals.

Mushroom rocks are formed in deserts. It is an erosional landform of arid regions. The mushroom rocks have a broad upper part and narrow base resembling an umbrella. The erosive power of wind is very high at a certain height from the ground level. The resistant rocks take the shape of a mushroom having large top and a small neck.

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. Unlike bauxite, magnesium, or manganese, it is not a metallic ore.

Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Igneous rocks occur in a wide range of geological settings: shields, platforms, extended crust, basins, and oceanic crust.

The Deccan Traps, which include the Maharashtra plateau and the Sahyadris, were formed by massive volcanic eruptions, resulting in igneous rock (specifically basalt).

Marble is a metamorphic rock formed from the metamorphism of limestone, a sedimentary rock, under high heat and pressure.

Igneous rocks are known as primary rocks as they are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust.

The Aravalli  range are the oldest fold mountains in India. The northern end of range continues as isolated hills and rocky ridges into Haryana state, ending in Delhi. The famous Delhi Ridge is the last leg of the Aravalli Range, which traverses through  South Delhi and terminates into Central Delhi
where Raisina hill is its last extension. It is one of the world's oldest mountain ranges. 

Regolith is a region of loose unconsolidated rock and dust that sits atop a layer of bedrock. On Earth, regolith also includes soil. It includes dust, soil, broken rock, and other related materials. It is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons.

Rock wastes, such as stone dust or crushed aggregate, are frequently used in the manufacturing of construction materials like bricks, tiles, and concrete blocks.

Weathering is the name given to the process by which rocks are broken down to form soils. Rocks and geological sediments are the main parent materials of soils (the materials from which soils have formed).

Most of the Marble rocks are located in the state of Madhya Pradesh.

Basalts are igneous rocks formed by the rapid cooling and solidification of lava on the Earth's surface.

• Rocks are the parent material for soil.
• Rocks are also found in form of ores which serve as a source of various metals.
• Rocks are the source of various minerals like phosphates and nitrates.
• Hence all are correct.

• Fossil fuels are obtained from sedimentary rocks and are formed under extreme temperature and pressure conditions.
• When the fossil sediments get compressed into the rocks, with passing time there is the gradual decay of the fossils under extreme temperature and pressure which converts fossils into fossil fuels deep inside.

• By dating the rocks in Earth's crust, as well as the rocks in Earth's neighbours, such as the moon and visiting meteorites, scientists have calculated that Earth is 4500 million years old.
• Option A is closest, thus it is correct answer.

Rocks do not remain in their original form for long but may undergo transformation. Rock cycle is a continuous process through which old rocks are transformed into new ones.

Igneous rocks are of two types, extrusive and intrusive. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate.

• Rock cycle is the transition of rocks of 3 basic types viz igneous, sedimentary and metamorphic into each other in a cyclic manner.
  
• Primary rock is an igneous rock which is formed after solidification of lava. It may then get eroded and settled as various layers to form sedimentary rocks. The sedimentary rocks get metamorphosised under high pressure and temperature beneath the earth crust which forms metamorphic rocks.
• Finally, all types of rocks may get subducted deep inside the earth were under extreme temperatures they get melted leading to the formation of liquid magma and the cycle repeats.
• Thus all options are part of this cycle and option D is correct.